“During the hearing, we introduced a lot of new data,” water authority Deputy General Manager John Entsminger said. “We submitted the only new data collected in the period between the last ruling and this one.”

“King has until late March to rule on the bulk of the water the authority hopes to pipe to Las Vegas through a multibillion-dollar pipeline network stretching more than 300 miles. Most of the water would come from Spring Valley, a vast basin just west of Great Basin National Park.

In an unusual move, King asked the authority and other official participants in last year’s six-week hearing to write their own versions of how his final ruling should read.

The authority would get no water at all under most of the draft rulings penned by opponents of the pipeline project.”

“In the northern states, its water supports cattle empires. In its southern stretch, especially in California’s Imperial County, the river irrigates deserts to produce America’s winter vegetables. And all along the way, aqueducts branch off to supply cities from Salt Lake City and Denver to Phoenix and Los Angeles. The metropolis closest to Lake Mead, Las Vegas, gets 90% of its water from this one source.

“That is why Las Vegas is a canary in the mine shaft, as Pat Mulroy, the boss of the Southern Nevada Water Authority, puts it. The Las Vegas valley gets its water through two long channels drilled through the rock. The first taps the lake at 1,050 feet (320 metres) above sea level, the second at 1,000 feet. Lake Mead’s water level is now near its record low, at 1,086 feet. Within a few years it could leave Las Vegas’s first intake, or even both, dry.

“The threat to Sin City is a good example of the four dimensions—physical, legal, political and cultural—of water in the West. For the physical, the standard response is to summon the engineers. Ms Mulroy already has them digging a third intake at 890 feet. Given the weight of the water on top, this is fiendishly difficult and will not be ready until 2014. Ms Mulroy also wants to pipe groundwater from the rural and wetter northern counties of Nevada to Las Vegas, but that has caused a vicious row.”